The invention relates to a process for preparing a suspension of coal particles in a hydrocarbon fuel. Such suspensions make excellent fuels, and if the suspended coal particles are small enough, can be atomized as a liquid fuel in a burner. For the preparation of the suspensions the amount and particle size distribution of the solid must be chosen such that a dynamically and, if desired, statically stable suspension is obtained wherein the particles do not segregate or agglomerate. The ultimately allowable viscosity, too, puts limits to the amount and shape of the solid material in these suspensions. Within the scope of these limits, it is, however, very well possible to prepare attractive fuels.
Those skilled in the art will recognize that the solid material has to be distributed as homogeneously as possible through the hydrocarbon fuel. With the preparation of the suspensions the latter requirement gives rise to problems. It is difficult to mix an amount of dry coal powder homogeneously with the required amount of hydrocarbon fuel. This calls for a relatively large amount of energy and expensive equipment, one problem being the abrasive character of dry coal powder.
For application of the suspensions as fuel, it is desirable that the coal particles contain as little ash as possible. Since most coals contain a relatively high percentage of ash, the coal often has to be de-ashed before it can be made into the suspension. De-ashing also requires much energy and expensive equipment. The present invention aims at a combination of these two unrelated treatments to achieve considerable savings.